A semiconductor integrated circuit using a conventional inductor includes, for example, the one shown in the Institute of Electronics, Information and Communication Engineers, Technical Report of IEICE, Vol. 93, No. 416, pp. 43 to 48 (1993). Since a spiral inductor shown in the paper can be formed on the same substrate together with a gallium arsenic high electron mobility transistor (GaAs HEMT), a low-noise preamplifier and the like built into a matching circuit having the spiral inductor have been realized.
[Non-patent document 1] The Institute of Electronics, Information and Communication Engineers, Technical Report of IEICE, Vol. 93, No. 416.
The inductor characteristic changes due to reasons such as the shape thereof and a difference in the process. For example, there may be a problem such that when the inductor is used in a signal transfer circuit, the inductor characteristic is shifted from an optimum value in a target frequency, thereby causing a decrease in receiver sensitivity. Such a problem becomes noticeable when the frequency is high. The inductor characteristic can be brought close to the optimum value to some extent by adjusting an applied bias, but there is a limitation.
In electronic equipment for which miniaturization is required, particularly, in mobile communication equipment such as a mobile phone and a car phone, miniaturization is also required for the parts used therein. Moreover, as the operation frequency increases, the circuit becomes more complicated, and hence, narrow deviation is required for the parts used therein. Actually, however, there is a deviation in the individual parts, and a circuit constituted by mounting these parts may not function. Accordingly, a method in which variable type parts are used for a part of parts group constituting the circuit, and the variable type parts are finely adjusted so as to make the circuit function has been employed. As one method, there is a case in which a variable inductor is used.
In a variable inductor disclosed in Japanese Unexamined Patent Publication No. Hei 8-162331, a plurality of looped conductors having an open end is provided in the vicinity of a spiral conductor, and an opening or short-circuiting switch is provided respectively to the open ends. It is explained therein that as a result, the inductance of the inductor decreases.
On the other hand, in the inductor disclosed in Japanese Unexamined Patent Publication No. Hei 9-153411, a first conductor pattern formed of two spiral conductor patterns and a first magnetic film covering the first conductor pattern are formed on one surface of an insulating substrate, and a second conductor pattern formed of two spiral conductor patterns and at least a second conductor pattern of a second magnetic film covering the second conductor pattern are formed on the other surface of the insulating substrate, and the conductor patterns on the opposite surfaces are connected to each other to form one coil, and by cutting the magnetic film, the inductance value is changed and adjusted.
[Patent Document 1] Japanese Unexamined Patent Publication No. Hei 8-162331
[Patent Document 2] Japanese Unexamined Patent Publication No. Hei 9-153411
In the above described conventional art, however, the circuit configuration including the coil becomes complicated.